Japanese maples can be quite sensitive to hot afternoon sunshine; the leaves can develop brown margins and eventually turn crispy and die. If this is what happened, you might want to consider moving your trees so that they are sheltered from hot afternoon sunshine. If they are already receiving shade and they suddenly wilted, the roots are distressed, perhaps from too much water. Daily watering will keep the soil too moist and as a result the roots can suffocate. Try thoroughly watering the soil, then allowing the top inch to dry out before deeply watering again. Hope your maples rebound!